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Genetic Deletion of Cis-Regulatory Elements to Dissect the Function of the Non-coding Genome in human Preimplantation Models.

Cis-regulatory elements coordinate gene expression in a spatially and temporally controlled manner and contribute to the establishment of distinct cellular states during development. A substantial proportion of transcriptionally active cis-regulatory elements in primate embryos originated from ancient retroviral integrations into the germline. These endogenous retroviruses, also known as long terminal repeat retrotransposons, retain intrinsic regulatory activity and are often species-specific, making them strong candidates for regulating species-divergent aspects of embryonic development. Ethical and legal restrictions on human embryo research have historically limited direct investigation of gene regulation during human embryogenesis. Human naive pluripotent stem cells and three-dimensional stem cell-based blastocyst models provide alternative systems for studying early developmental processes. This protocol describes the CRISPR-Cas9-mediated deletion of endogenous retrovirus-derived cis-regulatory elements in human naive pluripotent stem cells. Preassembled Cas9 and single-guide RNA ribonucleoprotein complexes are delivered by nucleofection, followed by single-cell cloning, PCR-based genotyping, Sanger sequencing, expansion, cryopreservation, and genomic stability assessment of the edited lines. The resulting wild-type, heterozygous, and homozygous or hemizygous deletion clones provide a platform for investigating the contribution of individual endogenous retrovirus-derived elements to gene regulation in human preimplantation models. This method enables direct functional interrogation of species-specific non-coding regulatory sequences and supports the study of transcriptional mechanisms involved in early human development.

Humans

Core passive and facultative mTOR-mediated mechanisms coordinate mammalian protein synthesis and decay.

The maintenance of cellular homeostasis requires tight regulation of proteome concentration and composition. To achieve this, protein production and elimination must be robustly coordinated. However, the mechanistic basis of this coordination remains unclear. Here, we address this question using quantitative live-cell imaging, computational modeling, transcriptomics, and proteomics approaches. We found that protein decay rates systematically adapt to global alterations of protein synthesis rates. This adaptation is driven by a core passive mechanism supplemented by facultative changes in mechanistic/mammalian target of rapamycin (mTOR) signaling. Passive adaptation hinges on changes in the production rate of the machinery governing protein decay and allows for partial maintenance of the cellular proteome. Sustained changes in mTOR signaling provide an additional layer of adaptation unique to naive pluripotent stem cells, allowing for near-perfect maintenance of proteome composition. Our work unravels the mechanisms protecting the integrity of mammalian proteomes upon variations in protein synthesis rates. A record of this paper's transparent peer review process is included in the supplemental information.

TOR Serine-Threonine Kinases

Generation of Transgene-Free Naive Human Induced Pluripotent Stem Cells from Somatic Cells Using a Modified Temperature-Sensitive Sendai Virus System.

The Sendai virus (SeV) vector system offers an efficient, nonintegrating approach to reprogram somatic cells into either naive or primed human induced pluripotent stem cells (iPSCs). Here, we describe a protocol to generate transgene-free naive iPSCs from human dermal fibroblasts (HDFs) and peripheral blood mononuclear cells (PBMCs) using a modified, temperature-sensitive SeV system. The method leverages LMYC in place of cMYC and an optional H1FOO-DD factor to enhance efficiency and uniformity, and employs a controlled temperature shift to facilitate vector clearance.

Humans

Modeling early gastrulation in human blastoids with DNA methylation patterns of natural blastocysts.

Blastoids are a promising model for studying early human embryogenesis, but current models have limitations in post-implantation development and lack comprehensive epigenetic assessments, especially regarding genomic imprinting. These issues can lead to failures in accurately modeling early embryonic development. In this study, we developed a high-fidelity blastoid model using 4 chemicals + leukemia inhibitory factor (LIF) (4CL) naive human pluripotent stem cells (hPSCs) (4CL blastoids). 4CL blastoids closely resemble human blastocysts in morphology and transcriptional profiles, exhibiting similar DNA methylation and gene imprinting patterns. By extending the 3D culture to 14 days, these blastoids mimic early gastrulation, demonstrating the specification and migration of cells. They also show the transcriptional signature of hemogenic angioblast (HAB) cells at Carnegie stage 6 (CS6). This model bridges pre- and post-implantation stages, offering valuable insights into early tissue formation and human development.

Humans

Generation of eight-cell embryo-like cells from human pluripotent stem cells.

Mammalian embryonic development is a highly orchestrated process initiated by the fusion of the oocyte with sperm to generate the zygote. In humans, the zygote remains transcriptionally quiescent until the major wave of zygotic genome activation (ZGA) occurs around the eight-cell (8C) stage (day 3 after fertilization). These cells and the derived morula cells are totipotent: they have the capacity to form a whole individual. Our understanding of human totipotency is very limited because of ethical concerns using embryos and the scarcity of material available for research. Recently, we established a controllable transgene-free methodology to generate totipotent eight-cell embryo-like cells (8CLCs) from human pluripotent stem cells (PSCs) in vitro. These 8CLCs are produced using a novel medium, formulated by us, containing specific chemical compounds and cytokines. Here, we provide a detailed protocol for inducing, isolating and characterizing 8CLCs generated with this medium. The induction process can be done either in a stepwise manner (primed-naive-8CLC) that requires only 5 d starting from naive PSCs or directly from primed PSCs, which takes ~7 d. The resulting 8CLCs exhibit transcriptional and epigenetic features resembling those of human 8C embryo cells. On the basis of our experience, we expect that an individual with ~1 year of experience working with human PSC culture would be able to carry out this protocol. Our approach provides a valuable model for studying human early embryogenesis, particularly the molecular events surrounding ZGA.

Journal Article